Browsing by Subject "Interference"

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    All-fiber all-normal-dispersion femtosecond laser with nonlinear multimodal interference-based saturable absorber
    (Institute of Electrical and Electronics Engineers Inc., 2019) Teğin, Uğur; Ortaç, Bülend
    Chong et al. demonstrated a stable passively mode-locked all-normal-dispersion fiber laser and pulse generation is attributed to the strong spectral filtering of chirped pulses, dissipative soliton pulses [1]. In the following years, with very-large-mode-area fibers the energy and power scalability of the dissipative soliton pulses is demonstrated. Recently, multimodal interactions are subject to device studies with various configurations. Nazemosadat et al. theoretically proposed a short graded-index multimode fiber segment in between single mode fiber as a saturable absorber [2]. On the other hand, with similar device structure an all-fiber bandpass filter is later presented both numerically and experimentally [3].
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    Linear precoder design for simultaneous information and energy transfer over two-user MIMO interference channels
    (Institute of Electrical and Electronics Engineers, 2015) Özçelikkale, A.; Duman, T. M.
    Communication strategies that utilize wireless media for simultaneous information and power transfer offer a promising perspective for efficient usage of energy resources. With this motivation, we focus on the design of optimal linear precoders for interference channels utilizing such strategies. We formulate the problem of minimizing the total minimum mean-square error while keeping the energy harvested at the energy receivers above given levels. Our framework leads to a non-convex problem formulation. For point-to-point multiple-input multiple-output channels, we provide a characterization of the optimal solutions under a constraint on the number of transmit antennas. For the general interference scenario, we propose two numerical approaches, one for the single antenna information receivers case, and the other for the general case. We also investigate a hybrid signalling scheme, where the transmitter sends a superposition of two signals: a deterministic signal optimized for energy transfer and an information carrying signal optimized for information and energy transfer. It is illustrated that if hybrid signalling is not incorporated into the transmission scheme, interference can be detrimental to the system performance when the number of antennas at the receivers is low.
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    Manoeuvring-target tracking with the Viterbi algorithm in the presence of interference
    (IET, 1989) Demirbaş, K.
    The Viterbi algorithm is used to track a target in the presence of random interference, such as jamming. A nonlinear target motion and an observation which is modelled in a spherical coordinate system are considered. The observation model is a nonlinear function of interference. The components of the state vector are the range, bearing angle, and elevation angle of the target location. The state vector is estimated, component-by-component, by a parallel use of the Viterbi algorithm in blocks. Simulation results, some of which are presented, have shown that the proposed estimation scheme performs well, whereas classical estimation schemes, such as the extended Kalman filter, cannot, in general, handle target tracking in the presence of random interference.
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    Performance limits on ranging with cognitive radio
    (IEEE, 2009-06) Dardari, D.; Karisan, Yasir; Gezici, Sinan; D'Amico, A. A.; Mengali, U.
    Cognitive radio is a promising paradigm for efficient utilization of the radio spectrum due to its capability to sense environmental conditions and adapt its communication and localization features. In this paper, the theoretical limits on time-of-arrival estimation for cognitive radio localization systems are derived in the presence of interference. In addition, an optimal spectrum allocation strategy which provides the best ranging accuracy limits is proposed. The strategy accounts for the constraints from the sensed interference level as well as from the regulatory emission mask. Numerical results are presented to illustrate the improvements that can be achieved by the proposed approach. © 2009 IEEE.
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    A physical model for acoustic signatures
    (A I P Publishing, 1980-01) Atalar, Abdullah
    A physical model is presented to explain the interference phenomenon that gives rise to the material‐dependent signature obtained from an acoustic reflection microscope. An approximate formula is derived for the peak separation of the characteristic response, and it agrees well with the experimental results.
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    Range estimation in multicarrier systems in the presence of interference: performance limits and optimal signal design
    (IEEE, 2011) Karisan, Y.; Dardari, D.; Gezici, Sinan; D'Amico, A. A.; Mengali, U.
    Theoretical limits on time-of-arrival (equivalently, range) estimation are derived for multicarrier systems in the presence of interference. Specifically, closed-form expressions are obtained for Cramer-Rao bounds (CRBs) in various scenarios. In addition, based on CRB expressions, an optimal power allocation (or, spectrum shaping) strategy is proposed. This strategy considers the constraints not only from the sensed interference level but also from the regulatory emission mask. Numerical results are presented to illustrate the improvements achievable with the optimal power allocation scheme, and a maximum likelihood time-of-arrival estimation algorithm is studied to assess the effects of the proposed approach in practical estimators.
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    Time-of-arrival estimation in OFDM-based cognitive radio systems
    (2010) Karışan, Yasir
    Cognitive radio (CR) systems can efficiently utilize the radio spectrum due to their ability to sense environmental conditions and adapt their communications parameters (such as power, carrier frequency, and modulation) so as to enable dynamic reuse of the available spectrum. In this thesis, theoretical limits on time-of-arrival (TOA) estimation are derived for CR systems in the presence of interference. Specifically, closed form expressions are obtained for Cramer-Rao bounds (CRBs) on TOA estimation in orthogonal frequency division multiplexing (OFDM) based CR systems in various scenarios. Based on the CRB expressions, an optimal power allocation strategy that provides the best possible TOA estimation accuracy is proposed. This strategy considers the constraints imposed by regulatory emission mask and the sensed interference spectrum. The maximum likelihood (ML) TOA estimator is derived for an OFDM-based signalling scheme, and its performance is investigated against the theoretical limits offered by the CRB expressions. In addition, numerical results for the CRBs and ML TOA estimator are obtained and the effects of the optimal power allocation strategy on the accuracy of ML TOA estimator are examined in the absence/presence of interference. The use of optimal power allocation strategy instead of the conventional power assignment scheme is demonstrated to provide significant gains in terms of the TOA estimation accuracy. Analysis of the performance sensitivity of the optimal power allocation strategy to the uncertainty in spectrum estimation is performed, and the performance of optimal power allocation is observed to be consistently superior to that of the uniform power allocation even for substantially high values of spectral estimation errors.
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    Working memory capacity: concurrent subtasks need not interfere
    (2022-10) Şengil, Gülsüm Özge
    Any extended task episode is subsumed by goal-directed programs that hierar- chically control its execution. We investigated the relationship between working memory capacity and the control instantiated by such hierarchical task entities across four experiments. In a new extended task consisting of subtask A and subtask B, participants first memorized the orientation of subtask A lines (let’s call this event mA), then memorized subtask B lines (mB), then recalled these B lines (rB), and finally recalled A lines (rA). The task structure was: mA-mB-rB- rA. Subtask A lines were thus held in mind during the execution of subtask B. Even though participants had to remember the orientation of lines in both cases, increased WM load of lines A only affected performance on subtask A and did not affect the performance on subtask B. In Experiment 2, four trials of Exp1 were organized into a complex 4-part task with the added condition that A lines of a part be recalled not in that part but in the next part. The task structure was: mA1-mB1-rB1—mA2-mB2-rB2-rA1—mA3-mB3-rB3-rA2—mB3-rB3-rA3. Load of A lines again did not affect B lines. Crucially, load of A2 and A3 lines did not affect the recall of A1 and A2 lines, respectively. In Experiment 3, in a design similar to Exp1, time constraint on mA and mB increased the interference across concurrent subtasks. Experiment 4 showed that increasing the similarity between subtask A and subtask B of Exp1 may increase the across-subtask in terference. We show that WM information of different concurrent subtasks can be maintained separately, perhaps as part of their goal-directed programs. And, encoding to these non-interfering stores, as well as retrieval from them, might depend on attentional and time-based mechanisms.